FOSSIL LAND SHELLS £5 



somewhat pinched, as if the surroundings had been less favorable to 

 their existence. The Lepachtinise do not require trees for their dwell- 

 ings, being the terrestrial group of the genus. 



Professor Lyons found similar shells on Punchbowl and writes as fol- 

 lows concerning another locality : 



" The most interesting find of fossil shells was in a volcanic tufa (primary) near 

 Pearl Harbor. Evidently the volcanic ash had been deposited in water, the shells 

 brought down in streams, possibly in freshets, and the material, which seems to 

 have had properties like those of Portland cement, set under water to form rock. 

 In a similar material there are preserved many impressions of leaves, apparently 

 like those of the existing forests." 



In the Annual, after remarking that one of these species still lives in 

 the Waianae mountains, Professor Lyons concludes that — 



" The fossils belong to a period previous to that of the receding of the ocean to 

 its present level. That event may have been coetaneous with the change of level 

 in the circumpolar area which marked the close of the great Glacial period, and 

 the evidences that our climate was, previously to that time, more humid than at 

 present are confirmatory of that view." 



Now that the Diamond Head breccia proves to be of Tertiary age, 

 additional interest will be given to the study of the development of these 

 land shells. 



Order op Events in the geological History of Oahu 



From the descriptions now presented it is possible to make out the 

 order of the principal events in the geological history of this volcanic 

 island. We are now satisfied with the existence of Tertiary deposits 

 antedating the rise of the earliest basaltic land, but will not consider 

 whether there may have been any rising of the ocean floor in connection 

 with the eruptions. 



1. At the base of Kaala igneous eruptions commenced under water to 

 accumulate sheets of basalt until finally the island of Kaala, a smooth 

 dome, rose above the waters, which slowly became covered by vegeta- 

 tion derived from distant regions. 



2. This dome became extensively channeled by streams produced as 

 now by the condensation of the moisture brought by the northeast trade 

 winds. Like existing islands under the same conditions, the erosion was 

 greater on the northeastern than southwestern sides. 



3. The island of Koolau came up quite near to Kaala in a similar 

 manner, and lava flowed down so as to conceal several hundred feet 

 altitude of the northeast flank of Kaala. Koolau extended out to sea 

 several miles farther to the northeast than at present. 



VIII— Bull. Geol. Soc. Am., Vol. 11, 1899 



